Technical Field
This application relates to medical devices, and more particularly, to vaso-occlusive devices used in the treatment of intracranial aneurysms.
Background of Related Art
An aneurysm is a localized, blood filled balloon-like bulge that can occur in the wall of any blood vessel, as well as within the heart. One endovascular treatment option for aneurysms is complete reconstruction of the damaged vessel using a vascular prosthesis or stent-graft. A stent-graft is an implantable tubular structure composed of two parts, a stent and a graft. The stent is a mesh-like structure made of metal or alloy which functions as a scaffold to support the graft. The graft is typically a synthetic fabric that is impervious to blood flow and lines the stent. Stent-grafts are not a treatment option for intracranial aneurysms due to the risk of cutting off blood flow to feeder vessels that may be vital for brain function. Stent-grafts can also be stiff, hard to deliver/retract, and can be highly thrombogenic within the parent vessel, all of which are undesirable features for intracranial aneurysm treatment. As a result, endovascular treatment of intracranial aneurysms has centered on packing or filling an aneurysm with material or devices in order to achieve a high packing density to eliminate circulation of blood, which leads to thrombus formation and aneurysm closure over time.
There have been a variety of materials and devices described for filling the sac of an intracranial aneurysm such as injectable fluids, microfibrillar collagen, polymeric foams and beads. Polymeric resins such as cyanoacrylate have also been used. Both are typically mixed with a radiopaque resin to aid in visualization. These materials pose a significant risk due to the difficulty of controlling dispersion and in retrieving them, if improperly or excessively delivered.
Mechanical vaso-occlusive devices are another option for filling an aneurysm. One type of mechanical vaso-occlusive device for the placement in the sac of the aneurysm is a balloon. Balloons are carried to the vessel site at the end of a catheter and inflated with a suitable fluid, such as a polymerizable resin, and released from the catheter. The main advantage of the balloon is its ability to effectively fill the aneurysm sac. However, a balloon is difficult to retrieve, cannot be visualized unless filled with contrast, has the possibility of rupture, and does not conform to varying aneurysm shapes.
Other types of mechanical vaso-occlusive devices are composed of metals or alloys, and biocompatible fibers, for example. Generally, the materials are formed into tubular structures such as helical coils. One of the earliest fibered coils was the Gianturco coil (Cook Medical). This coil was formed from a 5 cm length of 0.036″ guidewire (inner core removed) and featured four 2 inch strands of wool attached to one tip of the coil to promote thrombosis. This device was difficult to introduce into tortuous vessel sites less than 3 mm in diameter. This is generally because the coil was stiff or bulky and had a high coefficient of friction.
Chee et al. (U.S. Pat. No. 5,226,911) introduced a more deliverable fibered coil with fibers that were directly attached to the length of the coil body. This coil was designed for more tortuous anatomy by decreasing the amount of thrombogenic material being delivered with the coil. Other examples of coils are U.S. Pat. No. 4,994,069 to Ritchart et al.; U.S. Pat. No. 5,354,295 and its parent, U.S. Pat. No. 5,122,136, both to Guglielmi et al.
Materials can also be formed into tubes/strings/braided sutures (see, e.g., U.S. Pat. No. 6,312,421 to Boock; U.S. patent application Ser. No. 11/229,044 to Sepetka et al.; U.S. patent application Ser. No. 13/887,777 to Rees; U.S. patent application Ser. Nos. 13/552,616 and 10/593,023 both to Wu et al.), cables (see, e.g., U.S. Pat. No. 6,306,153 to Kurz et al.), or braids. Metal coils can also be covered by winding on thrombogenic fiber as described in U.S. patent application Ser. No. 12/673,770 to Freudenthal and U.S. Pat. No. 6,280,457 to Wallace et al.
Unlike other tubular structures, braided or polymer coils can be further divided into non-expandable and self-expandable devices. These devices can be made from materials such as textiles, polymers, metal or composites using known weaving, knitting, and braiding techniques and equipment. Included in the weave or the finished braid can be optional mono or multifilament fiber manufactured to impart additional features or effects (e.g., radiopacity and thrombogenicity).
Non-expandable braids (see, e.g. U.S. Pat. No. 5,690,666 to Berenstein et al.; U.S. Pat. No. 5,423,849 to Engelson et al.; and U.S. Pat. No. 5,964,797 to Ho) can act as the implant and be mainly metallic, polymer, or a combination of metal and polymer. In such designs, braids have some minimal space between the filaments (braid strands) resulting in open cell designs. In addition, tight, mostly metal braids employing such designs result in stiff structures which are difficult to track via catheter or risk injury to the vasculature. Also, metal braided structures may be rough to the touch if not covered or further processed.
These braids can be formed into secondary shapes, such as coils that have little or no inherent secondary shape, they can be dimensioned to engage the walls of the aneurysm, or they can have other shapes (e.g. random, “flower”, or three dimensional). These structures can also have a fiber bundle(s) in, or protruding from, the interior core made of natural fibers or thermoplastics infused with drugs to help with clotting (see, e.g., U.S. Pat. No. 5,423,849 to Engelson et al.; and U.S. Pat. No. 5,645,558 to Horton). Coiled braids can also be supplied with bio-active or other surface coatings (see, e.g., U.S. Pat. No. 6,299,627 to Eder et al.).
Non-expandable braids can also cover core or primary structures, such as coils or other braids (see, e.g., U.S. Pat. No. 5,382,259 to Phelps et al.; U.S. Pat. No. 5,690,666 to Berenstein et al.; U.S. Pat. No. 5,935,145 to Villar et al.; and U.S. Pat. No. 8,002,789 to Ramzipoor et al.). Much like the above braid structures, these covers have open cell designs (e.g., inner coil structure is visible through the braid).
Regardless of configuration, it is difficult to achieve high packing densities and rapid flow stagnation with these devices as they have open cell construction which allows at least some blood flow through the wall, may not compress adequately, and/or may have limited bend radii. If an aneurysm sac is not sufficiently packed to stop or slow blood flow, any flow through the neck of the aneurysm may prevent stasis or cause coil compaction, leading to recanalization of the aneurysm. Conversely, tight packing of metal coils in large or giant aneurysms may cause increased mass effect (compression of nearby tissue and stretching of aneurysm sac) on adjacent brain parenchyma and cranial nerves. Coil prolapse or migration into parent vessels is another possible issue with non-expanding devices, especially in wide neck aneurysms.
Braids may also be self-expanding and can be shaped into various forms such as a ball, a coil(s), and a combination braid-stent. Examples of self-expanding devices are disclosed in the following: U.S. Pat. No. 8,142,456 to Rosqueta et al.; U.S. Pat. No. 8,361,138 to Adams; U.S. patent application Ser. No. 13/727,029 to Aboytes et al.; U.S. patent application Ser. No. 14/289,567 to Wallace et al.; U.S. patent application Ser. No. 13/771,632 to Marchand et al.; and U.S. patent application Ser. No. 11/148,601 to Greenhalgh.
Self-expanding braids are expected to occupy all or substantially all of the volume of an aneurysm to obstruct flow and/or promote endothelization at the neck. A major problem for these designs is sizing. The implant has to be accurately sized so that upon expansion it occupies enough volume to fill the entire aneurysm, dome to neck. Undersized devices lead to insufficient packing as described above, whereas oversizing risks rupturing the aneurysm or blockage of parent vessel.
Neck bridges are yet another approach to treating intracranial aneurysms. They can be broken down into two categories: those that act as support to keep the coil mass from migrating into a parent vessel (coil retainer) and those that span the neck to obstruct flow into the aneurysm. Neck bridges that support the coil mass tend to be petal/flower shaped and span the neck of the aneurysm or placed between the parent vessel and aneurysm sac. Examples of neck bridges for supporting the coil mass are disclosed in the following: U.S. Pat. No. 6,193,708 to Ken et al.; U.S. Pat. No. 5,935,148 to Villar et al.; U.S. Pat. No. 7,410,482 to Murphy et al.; U.S. Pat. No. 6,063,070 to Eder; U.S. patent application Ser. No. 10/990,163 to Teoh; and U.S. Pat. No. 6,802,851 to Jones et al.
Neck bridges that obstruct flow through the aneurysm neck can be deployed either internal or external to the aneurysm and may not require deployment of embolization coils. Examples of intra-aneurysmal neck bridges with deployment at the base of the aneurysm sac with components extending into the neck are disclosed in U.S. Pat. No. 6,454,780 to Wallace; U.S. Pat. No. 7,083,632 to Avellanet et al.; U.S. Pat. No. 8,292,914 to Morsi; and U.S. Pat. No. 8,545,530 to Eskridge et al. Examples of neck bridges deployed external to the aneurysm (in the parent vessel) are disclosed in U.S. Pat. No. 6,309,367 to Boock; U.S. Pat. No. 7,241,301 to Thramann et al.; and U.S. Pat. No. 7,232,461 to Ramer; U.S. Pat. No. 7,572,288 to Cox; U.S. patent application Ser. No. 11/366,082 to Hines; U.S. patent application Ser. No. 14/044,349 to Cox et al.; U.S. Pat. No. 8,715,312 to Burke; U.S. Pat. No. 8,425,548 to Connor; and U.S. Pat. No. 8,470,013 to Duggal et al. Neck bridges can also have surface treatment to encourage neointima formation as disclosed in U.S. Pat. No. 6,626,928 to Raymond et al. Regardless of design, neck bridges pose several problems when treating intracranial aneurysms. The first major challenge is deployment of these devices, which requires the bridge to be maneuvered and often re-positioned over the aneurysm neck to assure complete coverage. Secondly, if recanalization occurs, any subsequent retreatment of the aneurysm will be hampered due to access being restricted by the neck bridge or one of its components.
Stents and flow diverters are similar to neck bridges in function, but are intended for parent vessel reconstruction and therefore run distal to proximal of the aneurysm, covering the neck. Such devices are deployed in the parent vessel and are intended to act as a physical blood flow barrier to induce sac embolization, stabilize embolic coils, and prevent coil protrusion and/or migration. Flow diverters, due to their relative low porosity (high coverage), can be used with or without coils and have been found to promote thrombus formation by restricting blood flow into the aneurysm sac. However, complications such as recanalization, delayed stent thrombosis, delayed aneurysm rupture, and stent migration have also been observed. An example of a stent is disclosed in U.S. Pat. No. 6,746,475 to Rivelli and a flow diverter is disclosed in U.S. Pat. No. 8,398,701 to Berez et al.
While the above methods attempt to treat intracranial aneurysms with minimally invasive techniques, there remains a need for a highly compliant and thrombogenic filler that blocks blood flow within the sac of the aneurysm without the drawbacks of current devices. For example, it would be advantageous to provide a device that achieves sufficient flexibility to enable advancement through the tortuous vasculature into the cerebral vasculature and achieves high packing densities while maintaining a high concentration of thrombogenic material. It would also be advantageous to provide such device which is simple in structure and simple to manufacture without sacrificing efficacy. Still further, since the device is designed for minimally invasive insertion, such device needs to be easy to deliver and deploy at the intracranial site as well as manufacturable in a small enough size for use in cerebral vasculature. All of this needs to be achieved with a construction that effectively packs the aneurysm without damaging the sac or other tissue while promoting rapid clotting and healing of an intracranial aneurysm with reduction in mass effect. To date, no device effectively achieves all these objectives, with current devices at best achieving one objective at the expense of the other.